1. Dual Active Bridge Series Resonant Converter with Pulse Modulation
Z. Pavlović
The main feature of the proposed modulation is the elimination of the switching losses of the active devices that allows operating the DAB SRC at high switching frequency (500 kHz, 1kW converter). Thus, the transformer design is more compact and the resonant inductor is entirely composed of the transformer leakage inductance; no external inductor is needed.
Selected application for concept validation
Project sponsored by
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Electrical power architecture of the ¨More Electric Aircraft¨
The architecture and the bus voltage levels established by the military standard MIL-STD-704
240 V : 290 V range (270 V nominal) for higher voltage bus and
the 22 V : 36 V range (28 V nominal) for lower voltage bus
1 kW 28 V – 270 V converter
Bidirectional
Paralleling capability
Concept
Goal: ZVS and ZCS operation of all the switches
High switching frequency
High efficiency
M1=M4
M2=M3
Fixed ratio between input and output voltage t
M5=M8=M6=M7
Bidirectional
DC-DC
transformer t
LV side bridge
Power transfer
HV side bridge V1 V2 t
nV1 M1 M3
vCR M5 M7 V1 Vb - + + + Va V1
iLR V2 - -
Vtank t
2Vb
-2Vb M2 M4
Power flow
Vtank = V2-V1 M6 M8
case 1
case 2
ZVS and ZCS in both bridges!
iLR t t0 t1 t4 t2
ZVS in the LV bridge
Coss discharged to vCR/ vCR much lower than Vb
Reducing zero current interval to minimum Optimum point operation
Load regulation by voltage difference Va - Vb
Experimental results
Experimental results with round wire transformer
imag
ETD49/25/16 core, N87 material
Voltage waveform vDS2 affected by the TO220 case parasitic inductances
ZVS, M2
@ 700 W output power
High magnetizing current, imag!
Higher conduction losses
Lower transformer efficiency due to gap
η = 85.9 %
Far distant from the expected 93 %!
Needed experimental validation with:
DirectFET case style switching devices
Improved layout (Q3D Extractor estimation loss: 11.6 W)
Planar transformer
ZVS, M6
CONCLUSIONS
The proposed modulation is a good solution for applications in two stage, high power isolated converters. The main feature of this modulation is the elimination of the power transistor switching losses in both full-bridge sides of the converter, full ZVS and approximately ZCS are achieved in all the switches. This allows for higher switching frequencies to be adopted and, consequently, it allows reducing the size of the magnetic components. The proposed solution requires frequency variation to control the delivered power. Another control variable is the intermediate bus voltage, VC; by changing this voltage the control frequency band can be narrowed. Therefore, a non-isolated
second stage is required to regulate the intermediate bus voltage while the proposed DAB SRC provides the electrical isolation and high voltage step.